I have seen fish from local lakes and rivers with 'growths' on their skin - I'd feel much better about at least cooking them before eating. Parasites are a threat too.
Eating fresh-water fish raw is a baaaad idea. Parasites thrive in freshwater, nothing caught in freshwater should be eaten without thoroughly cleaning and cooking it. Saltwater fish however, are another story, there are currently no known parasites that infect saltwater fish that are commonly harmful to humans. Think of Sushi... all that fish is tropical saltwater type fish. You dont see catfish/bluegill/walleye/pike/trout sushi do ya?
Most commonly seen in freshwater fish is "Black Grub". They say it's incapable of harming humans, but I dunno. Here's a DNR entry about it. http://www.michigan.gov/dnr/0,1607,7-153-10364_10950-27376--,00.html
Yup, "parasite city" in most if not all freshwater species and varieties..... On a more personal note: ( and.... it tastes like CRAP too!) Gave it a try, back in the early 80's.... Won't be doing that again!
Any muscle aches? Joint pains? If you ever ate raw freshwater fish you should see a doctor that specializes in parasitology. The little worm critters can stay in your body for decades.
No never eat anything like that raw. I eat sushi a lot but salt water fish have natural antibiotics and a very low chance of having parasites. Fresh water fish on the other hand is just asking for trouble. I know one of the survival "experts" did it on T.V but he also ate a pond snail. The guy is asking for unwanted guests i his body. Do you know what an infection in your digestive tact can do to you? Not pleasant unless you like having a colostomy bag attached to you for the rest of your life. It's not that hard or time consuming to cook something or even smoke it.